1. Field of the Invention
The present invention relates to an automatic dispenser, and particularly to an automatic dispenser having an adjustable dispensing head and being capable of determining the shape and mounting status of dispensing tips in the dispensing head.
2. Description of the Related Art
Dispensing liquid samples, reagents, or the like to sample vessels in small quantities is an operation frequently performed during testing and analysis in the field of biochemistry. The dispensing operation is performed by drawing the liquid into and ejecting the liquid from dispensing tips mounted in a dispensing head. The dispensing tips are normally a disposable type that can be replaced with new dispensing tips after each use.
Recently, the number of these dispensing operations has increased dramatically in biochemical testing and analysis. When performed manually, however, the operations are inefficient and can lead to such problems as the user forgetting to mount or improperly mounting the dispensing tips. As a consequence, we are now seeing a shift from manual dispensing operations to automatic dispensing.
A conventional automatic dispenser includes a tip rack in which a plurality of dispensing tips are arranged, a dispensing head for accommodating the dispensing tips and dispensing the liquid contained therein, and sensors for determining the existence of dispensing tips in the tip rack. By monitoring the existence of dispensing tips in the tip rack, the sensors can determine whether a dispensing tip has been mounted in a dispensing nozzle. For example, the sensor determines that a mounting error has occurred when a dispensing tip that should have been mounted in a dispensing nozzle remains in the tip rack. Accordingly, the automatic dispenser can detect the mounting errors for mounting dispensing tips in the dispensing head, as described in Japanese unexamined patent application publication No. HEI-11-295323, for example.
However, if either the tip rack or the sensors deviate from their prescribed positions in the automatic dispenser of Japanese unexamined patent application publication No. HEI-11-295323, the sensors do not perform detection at the correct positions. For example, if the sensors are offset from their prescribed positions so that the sensors monitor a gap between dispensing tips, then the sensors determine that there are no remaining dispensing tips, that is, that all tips have been mounted.
Further, the automatic dispenser of Japanese unexamined patent application publication No. HEI-11-295323 can detect only whether all dispensing tips have been mounted properly in the dispensing head. Accordingly, this automatic dispenser cannot detect an abnormality when the dispensing tips are not correctly mounted in the dispensing head or when the mounted dispensing tips have a different shape. Hence, if the user mistakenly disposes a different type of dispensing tip in the dispensing rack, for example, the desired amount of reagent will not be acquired.